Discharge tube



J. BRUIJNES DISCHARGE TUBE July 7, 1936.

Filed Aug. 21, 1934 6 nuhhhnv J l Patented July 7, 1936 UNITED STATES PATENT OFFICE slgnor to N. V. Philips Gloeilampeniabrieken,

Eindhoven, Netherlands Application August 21 1934, Serial No. 740,836

In Germany September 1, 1933 11' Claims.

The present invention relates to discharge tubes comprising an incandescent cathode and a gaseous filling comprising a vapor and possibly also an inert gas.

More particularly, my invention relates to such discharge tubes as are used for rectiflers, relay tubes, etc., in which preferably an oxide cathode is used, and a vapor, for instance, the vapor of: mercury, one or more alkaline metals or earths,

or an amalgam of mercury with one or more of the latter materials, with or without the addition of an inert gas, such as argon, neon, helium, etc., together with an amount of the material of which the vapor is used in non-vaporized form.

The latter, in the case of mercury vapor in connection with which I shall describe my invention, is an amount of liquid mercury, which may be provided at the bottom part of the discharge tube.

To insure the generation of mercury vapor at the desired pressure, the mercury must be heated to a sufficiently high temperature. This can be achieved, in a simple manner, by arranging the cathode in the vicinity of the liquid mercury,

which has also the advantage of providing a high vapor pressure in the space around the cathode and protecting the cathode against evaporation as well as from ion bombardment. This arrangement, however, has the drawback of causing the mercury to be contaminated by the materials evaporating from the cathode. When using, for instance, an oxide cathode, which is coated with barium oxide, the barium evaporates to a marked extent and forms an alloy with the mercury.

This contamination of the mercury brings about that the vapor pressure of the filling, at a given temperature, becomes considerably lower than when pure mercury is present, which reduc- 40 tion in pressure unfavorably affects the operating characteristics of the discharge tube.

Such contamination of the mercury is prevented in accordance with the invention, without losing these advantages which are derived from disposing the cathode in the immediate vicinity of the mercury, and thus utilizing the heat produced by the cathode for heating the mercury. Furthermore, according to the invention, a still higher protective vapor pressure can be obtained around the cathode than has been obtained in prior constructions.

In accordance with my invention I locate the incandescent cathode close to the surface of the material to be evaporated, for instance, of the liquid mercury, and separate it therefrom but provide means which cause the generated mercury vapor to be directed into the space surrounding the cathode.

Preferably, the cathode is disposed within a container which is open towards the anode, the 5 bottom of which container contacts with or immerses in the liquid mercury, and the side walls of which are provided with apertures for the passage oi the mercury vapor in the space surrounding the cathode. In addition, a bailie plate or 10 partition is provided, preferably secured to the cathode container above the level of said apertures and which partition substantially separates the liquid mercury from the discharge space of the tube. A gap provided between the parti- 15 tion and the surrounding container portion or apertures in the partition, permits the condensing mercury to flow back into the mercury reservoir along the wall of the container.

The above means insure a complete separa- 2o tion of the cathode and the liquid mercury, and

at the same time, as the cathode is disposed directly in the stream of the mercury vapor, it is thus surrounded with mercury vapor of comparatively high density. 26

With a construction according to my invention, it is possible to obtain a vapor pressure around the cathode which is even higher than in known constructions, in which the cathode is disposed above an open mercury reservoir and where the 30 mercury vapor could immediately expand above the level 01' the liquid mercury. In a construction, according to the invention, substantially the entire mercury vapor generated passes into the comparatively small space immediately surround- 35 ing the cathode, and while the cathode is separated from the liquid mercury, the vapor pressure surrounding the cathode has practically the same value as that existing at the surface of the liquid mercury and as practically all of the 0 mercury vapor has to pass through restrictions, it cannot immediately expand and thus it retains its high pressure around the cathode.

With such an arrangement, a vapor pressure of about 0.1 mm. of mercury can be readily ob- 45 tained in the space around the cathode and when this pressure is measured at an increasing distance from the cathode, this pressure drops very, quickly to a value of about 0.05 mm. mercury. 50

For this purpose the discharge tube may be given a large cooling surface or there may be provided between the cathode and anode spaces a separate condensation chamber of large diameter, which chamber communicates with the 55 anode chamber or anode chambers by means of narrow arms.

In a preferred form of construction, the partition member disposed between the mercury and the discharge space forms a cylindrical member which has a portion of smaller'diameter than has the adjacent portion of the tube envelope, so that the condensed mercury can flow back between the side of the cylinder and the tube wall; the cathode container and the partition member being secured to each other.

Since the cathode is located within a container which separates it from the mercury, it can be brought quite close to the surface of the liquid mercury. This insures a very efllcient vapor production without the danger of the mercury being contaminated. The bottom of the cathode container may be thereby immersed in the liquid mercury and may be immersed therein to such extent that the cathode itself'falls below the level of the mercury surrounding the container.

A simple way to form a reservoir for the liquid mercury is by giving the tube envelope a cupshaped bottom, which holds the mercury.

While the lead wires (supports) of the cathode may insulatingly pass through the liquid mercury, I prefer to introduce these wires at the tube end which is remote from the cathode. In latter case, means are provided to prevent displacement of the leads (supports), for instance, by securing same to the cathode container structure.

My invention is specially useful in connection with rectifier-s and relay tubes, operating at several hundreds volts and with currents of the order of several amperes; and can be applied to single phase as well as polyphase tubes.

The invention will be more fully described with reference to the accompanying drawing which represents by way of example some constructional embodiments thereof, and in which Figure 1 is a schematic sectional side view of the cathode end of a discharge tube embodying my invention.

Fig. 1-41 is a schematic sectional view of the cathode end of a discharge tube and shows another embodiment of the invention.

Fig. 2 is a side elevation, partly in section, of a three-phase rectifier tube embodying my invention and showing a somewhat modified form of construction.

The principle of the invention will be explained with regard to Fig. 1. The bottom end of the vitreous envelope I of the tube serves as a reservoir for the liquid mercury 2. A filamentary cathode 3, preferably an oxide cathode, is surrounded by a cup-shaped container 4 which is preferably of metal and is open on the top, which faces the anode. I

Secured, for instance, by welding, to the container 4 is a conical annular apron shaped partition member 5 which separates the liquid mercury from the discharge space, and which is provided aroimd its outer edge with a plurality of apertures 8, through which the mercury, which condenses in the discharge tube, can flow back to the mercury reservoir.

The cathode 3 is connected to lead-in wires 1 and 8, which also serve as supports and which are surrounded by insulating tubes 89, and are insulated thereby from the mercury. The outside connections to the lead-in wires are by means of metal discs 33-30 preferably of chrome-iron fused in the envelope wall and to which are welded or otherwise secured outer leads 3| and 32. The support-lead wires 1-43 are secured, for instance,

by welding, to the discs 3030 whereby the wires 3| and 32 are electrically connected with the support-lead wires 1 and 8 respectively. The vitreous portion of the container I is preferably fused or otherwise hermetically joined to the insulating tubes 9-9 by the portions shown at 33-43.

The container 4 is provided with a plurality of side apertures I which fall'below the junction of the partition 5 with the container 4, but above the level of the liquid mercury 2.

Practically all of the mercury vapor generated at the surface of the liquid mercury passes through apertures in into the space surrounding the cathode. In this manner a comparatively high vapor pressure is set up in the neighborhood of the cathode which pressure protects the cathode against disintegration by vaporization as well as by impact from ions of the discharge. Thus a long life of the cathode is insured.

It should be noted that between the envelope I of the tube and the partition 5, only so much space is left, for instance, by means of the apertures 6, as is necessary to permit the condensed mercury to flow back along the tube walls to the reservoir.

By rearranging the parts of Fig. 1, the cathode can be located below the surface of the mercury. Such a construction is shown in Fig. l-a, which is similar to Fig. 1; similar parts being designated by the same reference numerals. In Fig 1-a the container 4 is sufliciently far immersed into the mercury 2 so that the cathode 3 lies below the surface of the mercury. The partition 5 and apertures 10 are arranged in the same position relative to each other and to the surface of the mercury, as in the construction shown in Fig. 1.

Referring to Fig. 2, the arrangement of. the cathode 3 with respect to the liquid mercury 2 is similar to that in Fig. 1. The tube envelope l is of vitreous material and is provided with three arms 35-35 and with a cup-shaped bottom portion l2 at the cathode end and with a reduced diameter portion [5 on the end opposite to the cathode. The bottom portion l2 serves as a reservoir for the mercury. The cathode 3 is again provided in a cup-shaped container 4', the lower portion of which has a reduced diameter and the bottom I l of which is immersed in the liquid mercury, so that a strong heating of the mercury occurs due to the heat from the cathode being transferred by the bottom II to the liquid mercury.

The partition 5, in this construction, forms a cylindrical sleeve secured, for instance, by welding, to the cathode container 4' and is partly immersed in the liquid mercury, thereby separating the major portion of the liquid mercury from the dischargespace. Some of the mercury, however, falls outside of the cylinder 5"as shown at 34-34, this mercury being in communication with the main mercury body around the lower end of the sleeve 5'.

The upper portion of cathode container 4' is outwardly flared, as shown at l3, so as to further protect the mercury from disintegrated material.

The lead wires 1' and 3 of the cathode are supported from the end l5 of the tube, and are surrounded by tubes l4-l4 of steatite or other suitable insulating material. The outside leads 3l-32 are connected to lead wires 1' and 8' respectively in a manner similar to that shown in Fig. 1 or in other suitable ways.

A support in the form of a metal wire I6 is insulatingly secured to the end I! of the tube and carries a plurality of cross-supports II which Cil engage the steatite tubes "-44, keeping them in proper spaced relationship. The container 4' is also connected to steatite tubes ll-ll by means of supporting wires l8-l8 and is also connected to the wire Hi.

The cup-shaped bottom portion I2 01' the envelope, limits the lateral displacement of the cylinder 5', the latter forming an interconnected structure with the cathode container 4, the steatite tubes I l-I4 and the cathode 3, thus preventing lateral displacement of the cathode.

In addition, rollers lB-IQ mounted at the bottom edge of the cylinder 5' serve for the proper centering of the cylinder in the envelope end l2.

The wire'lS, which is insulatingly supported from the tube end l5, can be connected to a suitable electrical potential, for instance, by means of a wire 20 sealed through the container at 2|. As the wire I6 is connected with the cathode container 4', the latter assumes the potential applied to wire I 6. This potential, if desired, may be higher than the cathode potential, whereby the cathode container 4', can be used as an ignition electrode for initiating the main discharge.

The three arms 35 of the discharge tube (of which only two show in the drawing) contain each an anode 22, the lead wires iii-36 of which are insulatingly surrounded by steatite tubes 23-43.

In order to further protect the point at which the supply wire and the steatite tube are connected to the anode, the rear portion of the anode is surrounded by a cylinder 24, which may consist of metal gauze, so that the heat developed in the anode can be readily dissipated by radia-- tion, whereby the cylinder 24 also acts as a screen against back discharges.

Preferably, all of the metal parts within the discharge tube, which are or may be subject to contact with the mercury, are made of a material which is unaffected by mercury, for instance of iron or chrome-iron, or when using metals as copper or zinc, these are preferably provided with a protective coating, for instance with a chromium layer.

While I have described my invention on hand of a specific embodiment in a specific application, I do not wish to be limited thereto, but desire the appended claims to be considered as broadly as permissible in view of the prior art.

What I claim is:

1. A discharge tube having an envelope, an incandescent cathode and a gaseous filling therein, said filling comprising a vapor, a supply for said vapor consisting of the material thereof in a non-vaporized state, said cathode being disposed in the immediate vicinity of said supply to vaporize same, and a separating member between said cathode and said supply, said'member comprising means disposed in the immediate vicinity of the cathode and directing in a substantially free manner substantially the entire vapor generated by said supply directly from the surface of the supply into the space surrounding the cathode.

2. A discharge tube having an envelope, an incandescible oxide cathode and a gaseousfilling therein, said filling comprising mercury vapor, a supply of liquid mercury in said envelope, said cathode being disposed in the immediate vicinity of the mercury and heating said mercury to vaporize same, and a separating member between said cathode and said liquid mercury, said member comprising means disposed in the immediate vicinity of the cathode and directing in a substantially free manner substantially the entire vapor generated by said supply directly from the surface of the supply into the space surrounding the cathode.

3. A discharge tube having an envelope, an 5 incandescent cathode and a gaseous filling there in, said filling comprising a vapor, a supply for said vapor consisting of the material thereof in a non-vaporized state, said cathode being disposed in the immediate vicinity of said supply 10 and in intimate heat transferring relationship thereto to vaporize same, and a separating member between said cathode and said supply, said member being provided with apertures in the immediate vicinity of the cathode to allow sub- 15 stantially the entire vapor generated by said supply to pass in a substantially free manner from the space containing the supply directly into the space surrounding the cathode.

4. A discharge tube having an envelope, an 20 incandescent oxide cathode and an anode, a discharge space being formed between said cathode and anode, a gaseous filling comprising mercury vapor, liquid mercury disposed in said envelope, said cathode being disposed in the immediate vi- 5 cinity of said liquid mercury, a container surrounding the cathode and being open towards the anode, said container being provided with apertures in the immediate vicinity of the cathode to permit the mercury vapor to pass in a sub- 30 stantially free manner from the surface of the liquid mercurv directly into the space within the container, and a member interposed between the liquid mercury and the discharge space to substantially separate same from each other. 35

5. A discharge tube having an e'nvelope,-an incandescent cathode and an anode, a discharge space being formed between saidcathode and anode, a gaseous filling comprising mercury vapor and liquid mercury disposed in said envelope, said cathode being located in the immediate vicinity of said liquid mercury, a container surrounding the cathode and being open towards the anode, said container being provided with apertures for the passage of the mercury vapor into the cathode container, and an annular member interposed between the liquid mercury and the discharge space to substantially separate same from each other, said member being secured to the cathode container above the level of said apertures. 50

6. A discharge tube having an envelope, an incandescent oxide cathode and an anode, a discharge space being formed between said cathode and anode, a gaseous filling comprising mercury vapor, said envelope having a cylindrical bottom portion, liquid mercury disposed in said bottom portion, said cathode being located in the immediate vicinity of said liquid mercury to vaporize same, a cup-shaped member separating the cathode from the liquid mercury and having a hollow cylindrical projecting portion immersed in the mercury and substantially separating same from the discharge space, said cylindrical portion being so spaced from the bottom portion of the envelope as to permit the mercury which condenses in the tube to fiow back to the liquid mercury.

'7. A discharge tube having an envelope, an incandescent cathode and an anode, a discharge space being formed between said cathode and anode, a gaseous filling comprising mercury vapor, liquid mercury disposed in said envelope, a. container surrounding the cathode and having a bottom portion immersed in said mercury, and apertures in said cathode container located above posed below the level of said apertures and below the level or the mercury surrounding the cathode container.

8. A discharge tube having an envelope, an incandescent oxide cathode and an anode, a discharge space being formed between said cathode and anode, a gaseous filling comprising mercury vapor, said envelope having a cup-shaped bottom portion, liquid mercury disposed in said bottom portion, said cathode being disposed in the immediate vicinity of the liquid mercury to vaporize same, a container closely surrounding the oathode, said container having an aperture in the immediate vicinity of the cathode and a bottom portion in intimate heat-transferring relationship with said liquid mercury, and means separating said liquid mercury from the discharge space and directing in a substantially free manner substantially all the vapor generated at the surface 01 the liquid mercury directly through the apertures oi. the container and into the space surrounding the cathode.

9. A discharge tube having an envelope, an incandescent cathode and a gaseous filling therein, said filling comprising a vapor, a supply for said vapor consisting of the substance of the vapor in a non-vaporized state disposed at one end of the tube, said cathode being disposed in close heat-transferring relationship to said supply and heating the same, a member substantially separating said cathode from said supply,

,671 the level or said mercury. said cathode being disand conductive members supporting said cathode from the end or the envelope remote irom the end occupied by said supply.

10. A discharge tube having an envelope, an

incandescent cathode and a gaseous filling there- 5 in, said filling comprising a vapor, a supply for said vapor consisting of the substance oi the vapor in a non-vaporized state disposed at one end of the tube, said cathode being disposed in close heat-transferring relationship to said supply and heating the same, a member substantially separating said cathode from said supply, conductive members supporting said cathode from the end 01 the envelope remote from the end occupied by the supply, and guiding mem- 1s bers to prevent displacement of said conductive members.

11. A discharge tube having an envelope, an incandescent oxide cathode and a gaseous filling therein, said filling comprising a vapor, a supply so for said vapor consisting of the material thereof in a non-vaporized state, said cathode being disposed in the immediate vicinity of said supply to vaporize same, a cup-shaped member of conductive material separating said cathode and said 25 supply and surrounding the cathode, said cathode being provided with leads for the passage of a heating current through the cathode, and means to connect said member to an electrical potential which is not the cathode potential. 80

J OHANNES BRUIJNEB. 

